1. Technical Field
The present invention relates to printers, and particularly relates to an alignment system and techniques for vertical alignment of a printhead cartridge performing bidirectional printing in a serial printer.
2. Related Art
Conventional printer such as a dot matrix printer, inkjet printer and plotter includes a printhead having an array of nozzles mounted on a carriage for printing a plurality of rows of dots in a single scan of a movable print carriage across a printable medium. Typical printers print information serially one letter per unit time and can be unidirectional or bidirectional. Bidirectional printers can print information on a printable medium in both directions, that is, from left to right of a first row, and then from right to left of a second row next to the first row. As a result, a printing speed of a bidirectional printer is twice as fast as that of a unidirectional printer which can only print information in one direction and has a carriage which must be returned to a starting position for each row.
A printhead is typically mounted in a print cartridge within an assembly which is mounted on the carriage of the printer/plotter. Generally, full color or black and white printing or plotting requires that the carriage supporting the printhead be precisely aligned so as to begin printing information on a printable medium in each scan axis direction. Otherwise, any misalignment of the carriage will result in a misregistration of print images, particularly when the printer is a multi-color type of printer. Unfortunately however, mechanical misalignment of the carriage in the printable scan axis (i.e., x-axis) and in the carriage scan axis (i.e., y-axis) is common in conventional printers.
Conventional techniques for alignment of printhead of typical printers are disclosed, for example, in U.S. Pat. No. 5,600,350 for Multiple Inkjet Print Cartridge Alignment By Scanning A Reference Pattern And Sampling Same With Reference To A Position Encoder issued to Cobbs et al., U.S. Pat. No. 5,448,269 for Multiple Inkjet Print Cartridge Alignment For Bidirectional Printing By Scanning A Reference Patternissued to Beauchamp et al., U.S. Pat. No. 5,451,990 for Reference Pattern For Use In Aligning Multiple Inkjet Cartridge issued to Sorenson et al., U.S. Pat. No. 5,404,020 for Phase Plate Design For Aligning Multiple Inkjet Cartridges By Scanning A Reference Pattern issued to Cobbs, U.S. Pat. No. 5,350,929 for Alignment System For Multiple Color Pen Cartridges issued to Meyer et al., U.S. Pat. No. 5,297,017 for Print Cartridge Alignment In Paper Axis issued to Haselby et al., and U.S. Pat. No. 5,250,956 for Print Cartridge Bidirectional Alignment In Cartridge Axis issued to Haselby et al., in which software is incorporated into the printer for permitting a user to perform vertical and horizontal alignment of a printing position of a printhead via a predetermined test pattern. A series of vertical and horizontal test line segments is utilized by the user to perform vertical and horizontal alignment operations of the print cartridge. The user's visual confirmation is required when the printhead is aligned with respect to the test line segments. Since the user is required to confirm alignment operation, I have observed that the accuracy of such an alignment cannot be trusted. In addition, extra time and effort are required to align accurate vertical lines for bidirectional printing.